Thermally operated protective devices for polyphase currents



United tates Patent Ofiice THERMALLY OPERATED PROTECTIVE DEVICES FOR POLYPHASE CURRENTS Eusebe Bout-dean, Nanterre, France, assignor to La Telemecamque Electrique (Socit Anonyme), Nanterre, France, a company of France devices for polyphase currents.

A known form of thermally operated device includes which is heated by some or all of the current flowing in The strips are heated directly or indirectly However, existing devices of the kind just described have one disadvantage in that no protection is obtained on failure or underloading of one or more of the current phases.

It is an object of the present invention to provide a thermally operated protective device for polyphase currents which does not sulfer from the disadvantage referred to above.

In accordance with the present invention a thermally operated protective device for polyphase currents includes thermally responsive means for each current phase and a common control member which controls the current supply, the arrangement being such that overloading of at least one of the current phases causes the thermally responsive means appropriate to that phase to operate the common control member to cut off the current supply and which also includes means operatively connected to each thermally responsive means which operate the common control means to cut off the current supply on failure or predetermined underloading of at least one of the current phases.

In one particular embodiment of the invention in which the thermally responsive means are bimetal strips arranged in the same plane, each strip carries a pivoted lever. Movement of the bimetal strip due to overloading causes a free end of the strip to operate the control member. Failure or underloading causes the free end of the bimetal strip to pivot the lever and so operate the control member. Conveniently the strips may be arranged close and parallel to one another and the levers may have projections which bear on supports attached to adjoining strips.

In the case of a protective device for a 3-phase current supply, three bimetal strips are arranged side by side. The outer strips each have a short lever which is pivoted between two uprights on the strip and which bears and pivots on the support carried by the central strip. That strip has two levers pivotally mounted between uprights secured to it and which bear and pivot on supports carried by the outer strips. Thus protection is assured in the case of failure or underloading of one of the current phases or failure of any pair of phases.

As an example of the invention a .protective device in accordance therewith and suitable for a 3-phase supply ration of the contact studs 6,

2,713,621? Patented July 19, 1955 will now be described in greater detail with reference to the accompanying drawings in which:

Fig. 1 is a view of part of a device suitable for a three phase supply.

Fig. 2 is a plan view of part of Fig. 1.

Fig. 3a is a section along the line III-III of Fig. 2.

Fig. 4a is a section along the line IVIV of Fig. 2.

Figs. 3b and 4b, which correspond with Figs. 3a and 4a, show the operation of the apparatus in the case of a failure of the supply on one of the phases.

The apparatus shown in Fig. 1, which is intended for three phase current, comprises, in a casing 1, three par- E3, the upper faces of which, when viewed as in Fig. 1, are in the same plane When their temperatures are equal.

In the construction illustrated, the bimetal strips are partially slotted and are supported on a ledge 8 which and to which they'are fixed by means of bolts (not shown) which traverse the apertures B1, S1, B2, S2, B3, S3, and which simultaneously form the connecting terminals of the device. The current of each phase enters by one of the terminals E1, E2, E3, flows through each bi-metal strip, and emerges by way of the corresponding terminal S1, S2, S3. Each bimetal strip is therefore directly heated by the whole of the current of the relevant phase. The bimetal strips need not he slotted, and may be heated indirectly by means of resistance elements or may be heated directly or indirectly by a current which is only a part of the main phase current, the part being obtained, for example, by means of a current transformer.

The free ends of the bimetal strips co-operate with a rial, clarity in the drawing, the plate 2 is shown removed from its normal position as indicated by the dash-dotted lines. Normally the trunnions 3 pivot in the apertures 4 0f the casing 1.

Also mounted for rotation on the trunnions 3 is a conducting strip 5 carrying at its end a contact-stud 6 which, when the plate 2 is not operated by the bimetal strips, is in contact with a contact-stud 7 carried at the end of a second conducting strip 9.

It will be supposed that an auxiliary electric circuit connected to the strips 5 and 9 controls, for example, a contactor which controls the current supply of apparatus to be protected by the device and therefore the current for heating the bimetal strips B1, B2 and B3.

The precise manner in which the plate 2 controls the main supply current is not of importance and therefore the contact studs 6 and 7 are only shown diagrammatically in Fig. 1, but it will be understood that clockwise movement of the plate 2 on the trunnions 3 causes sepa- 7 to operate the apparatus controlling the main supply.

The plate 2 may in fact control any other contact arrangement, more particularly contacts of which the opening is rapid or which may be mechanically connected to the apparatus controlling the polyphase supply.

As may be seen in the drawings the upper face of each of the bi-metal strips B1, B2 and B3 carries small uprights which form mountings 16 which support the pivot or pivots 17 of levers L1, L2, L'z and L3 cut from sheets of insulating material and'arranged edgewise in relation to the bimetal strips B1, B2 and B3.

The bimetal strip B1 thus carries a lever L1 which extends towards and whose end B2 and which has a projecting portion A1 which rests on a strip T2 fixed to the lower face of the bimetal strip B2. Similarly the bimetal strip B3 carries a lever L3 which extends toward and whose end rests on the bimetal strip B2 and has a projecting portion A3 which is supported on the opposite side of the strip T2. The central bimetal strip B2 has two levers L2 and L'2 extending in opposite directions, the ends of which rest on the bimetal strips B1 and B3 respectively while the projecting portions A2 and A'2 of the levers bear on the strips T1 and T3 of the bimetal strips E1 and B3. The free ends of the levers have projecting portions C1, C2, C2, C3 which are situated in the same plane when the bimetal strips are at the same temperature and which are in contact with the lower face of the plate 2 as seen in the drawings.

' When 'one or more of the bimetal strips B1, B2, B3 is over-heated, it tends to bend in the direction of the plate 2 and exert a force on the plate by way of the end projecting portions C1, C2, C2, C3 of the levers.

If it is now assumed that one of the bimetal strips is cooled, through failure of the supply, in relation to the other two bimetal strips, an upwardly directed force is likewise exerted on the plate 2. If, for example as shown in Fig. 3b, the bimetal strip B1 moves in the direction of the arrow F, the end C1 of the lever L1 moves upwardly due to the pivotal movement of the lever L about the point of contact between the portion A1 and the strip T1 and moves the plate 2 upwardly. A similar action occurs if the bimetal strip B3 is cooled. If, however, the bimetal strip B2 is cooled in relation to the bimetal strips B1 and Ba, the two levers L2 and U2, bearing on the pads T1 and T simultaneously act through their ends C2 and O2 on the plate 2.

If it is assumed that only one of the phases can fail at a time, one of the two levers L2 or L'2 is unnecessary. However, it is usually necessary to take account of the possibility of the simultaneous underloading of two phases, the supply of the installation to be protected continuing in this case by the third of these phases, returning via neutral or earth.

If the simultaneously underloaded phases correspond to the bimetal strips B1 and B3, the tripping of the apparatus takes place as explained with reference to Fig. 3b. If, however, the underloaded phases correspond to the central bimetal strip and to one of the end bimetal strips, the two levers L2 and U2 are needed on the bimetal strip B2 in order to ensure tripping in every case.

Thus, the four levers L1, L2, U2 and L3 enable every contingency to be guarded against, either of excess of current failure of the supply or underloading of one or more phases.

It will be noted that, since the supporting projecting portions A1, A2 etc. of the levers are very close to the axes 17 of these levers, of the said levers is considerably magnified in relation to the relative movement of the free ends of two adjacent birnetal strips. The device is therefore very sensitive to balancing faults between phases.

What I claim is:

1. In a protective device for use with a plurality of electric circuits to be simultaneously interrupted if the current in any one of said circuits either exceeds a predetermined value or falls below a second predetermined value, the combination of a thermally responsive element operatively connected to each of said circuits, said elements being located adjacent one to the other and having portions moving in the same direction in response to excessive current values, a movably mounted control member having a portion located within the limits of motion of said moving portions of said elements and moved in said direction by said portions in response to excessive current the movement of the free end l values, said control member thereupon being eifective to v interrupt all of said circuits, and insulating levers pivotally mounted on each of said portions of said elements and between said elements and said control member, each of said levers further resting on means firmly connected to said portion of the adjacent element, whereby movement of any of said portions of said elements in said direction through a shorter distance than the movement of said portions of adjacent elements due to current falling below said second predetermined value raises theend of said lever in said direction to move said control member in said direction and interrupt all of said circuits.

2. In a protective device for use with a plurality of electric circuits to be simultaneously opened if the current in any one of said circuits either exceeds a predetermined value or falls below a second predetermined value, the combination of a thermally responsive strip element operatively connected to each circuit and having a free end portion moving in a given direction in response to excessive current and all of said free end portions extending in the same plane under similar conditions and moving in the same direction in response to excessive current, a pivotally mounted control member having an end portion extending in the path of movement of said free end portions in response to excessive current and displacement of said end portion of said control member in said direction operating an auxiliary circuit controlling all of said first-mentioned circuits, and an insulating lever pivotally mounted adjacent said free end portion of each of said strips and between said strip and said control member, said lever further extending from the strip on which it is mounted to an adjacent strip and engaging means firmly connected to said adjacent strip and having a free end portion actuated toward said control member when said adjacent strip is nearer said control member than the strip on which said lever is mounted, whereby said control member operates said control circuit both in response to excessive current in any circuit and in response to failure of any circuit to carry current of said second predetermined VaillQ.

3. in a device providing thermal protection against overloading or underloading of any of a plurality of electrical circuits, a bimetal thermal responsive strip operatively connected to each circuit, said strips being mounted each by one of its ends and extending parallel one to the others and all in the same plane when the currents of their circuits are at predetermined values, said strips further having free end portions moving in the same direction in response to overloads of their respective circuits, a control plate pivotally mounted with its free end portion in the path of motion of said end portions of said strips and moved by any of said free end portions upon the overloading of the respective circuit, said control plate controlling all of said circuits, each of said strips further having pivotally mounted on said free outer end and between the latter and said plate an insulating lever extending from said strip toward an adjacent one of said other strips, each strip further having rigid means firmly connected thereto and engaging each lever extending theretoward from an adjacent strip, said strips, means and levers being so related as to move the free end of any lever toward said control plate when r the strip mounting said lever is more distant from said plate than the strip mounting said means, and said free end of said lever actuating said control plate to control said circuits when the strip mounting said lever is a predetermined amount more distant from said control plate than the strip mounting said means.

4. A thermally operated protective device for use with three phase current, comprising the combination of three thermally responsive bimetal strips each strip being series connected in the circuit of its respective phase, said strips being slotted longitudinally for the major portion of their length from one end and being connected to said circuits at said end and the opposite ends of said strips extending freely therefrom, said strips further being parallel and extending in a common plane when at the same temperature and said free ends moving in the same direction in response to overloads of their respective circuits, a control plate pivotally mounted in overlying relation to said strips, the free end of said plate lying in the path of said strip ends when the latter move in response to overl0ad and. being movable by any of said ends and such motion of said plate being effective to open all of extension firmly connected thereto and said levers of said said circuits, two insulating levers pivotally mounted near outer strips resting on said latter extension, all of said the free end of the centrally located strip and between levers further having free ends moved toward said plate said strip and said plate and one of said levers extending by said means when the end of a strip mounting said from said strip toward each of the outer strips, each of 5 means is nearer said plate than the end of the strip said outer strips having an extension firmly connected mounting said lever.

thereto and said levers each having a portion resting on said extension of said strip toward which said lever References Cited m the file of this patent extends, and an insulating lever pivotally mounted on UNITED STATES PATENTS said free ends of said outer strips and between said strips 10 1,652,527 Hodgkins Dec. 13, 1927 and said plate and extending toward said centrally 10- 2,177,775 Jackson O 31, 1939 cated strip, said centrally located strip further having an 2,547,604 Sharp Apr. 3, 1951 

